Field of the Invention
The present invention relates to a workpiece conveyer apparatus of a machine tool, and more particularly to a conveying and processing technology for performing a series of operations of workpiece conveying and processing steps including delivery and discharge of a workpiece outside of a machine, and loading and unloading of a workpiece into or out of workpiece conveying means inside of a machine, in a machine tool such as a surface grinder having a grinding wheel for plane grinding of a workpiece.
Description of the Related Art
For example, a surface grinder having a grinding wheel for plane grinding of a workpiece is designed to perform exchanging (loading, unloading) workpieces mutually between a delivery machine for delivering workpieces, a discharge machine for discharging workpieces, and a surface grinder, automatically by the workpiece conveying and processing device.
A workpiece conveyer apparatus of this kind has, for example, as disclosed in Japanese Patent Application Laid-open Publication No. 2002-130421, a so-called double hand type slider comprising two work hands for loading and unloading a workpiece. This slider slides and moves on moving rails by means of a drive source, and the work hands are positioned and stopped at every specified processing station (delivery station, in-machine station, discharge station, etc.), and the workpieces are exchanged among the processing stations.
In a general workpiece conveyer apparatus of a machine tool, not limited to delivery, in-machine, and discharge stations, as shown in FIG. 8A, in total, five stations are often disposed such as delivery, rotation phase fixing, in-machine, inspection and measurement, and discharge stations S1, S2, S3, S4, S5, and the interval of these stations S1, S2, S3, S4, S5, that is, conveying pitches p are mutually equal (p1=p2=p3 p4).
By the simple so-called pick and place system of the double hand slider, that is, only by the lifting operation and placing operation by the work hands, a workpiece at a certain station is moved to a next station.
Incidentally, since the required space is different among the five stations S1, S2, S3, S4, S5, in particular, for the purpose of shortening the dimension of the entire facilities of the apparatus, it is considered effective means to define the distances among these five stations S1, S2, S3, S4, S5 at unequal pitches instead of equal pitches.
For example, as shown in FIG. 8B, conveying pitch p1 between delivery station S1 and rotation phase fixing station S2 outside of the machine and conveying pitch p4 between inspection and measurement station S4 and discharge station S5 are set smaller than conveying pitch p2 between rotation phase fixing station S2 and in-machine station S3 and conveying pitch p3 between in-machine station S3 and inspection and measurement station S4 (p1=p4<p2=p3).
However, to correspond to such unequal pitch conveying among these five stations S1, S2, S3, S4, S5, by using an expensive NC slider as the slider, it is necessary to employ a method of transferring workpieces by sequentially exchanging the workpieces at stations S1, S2, S3, S4, S5 by this NC slider and double hands of this slider. As a result, to transfer all workpieces at stations S1, S2, S3, S4, S5, as described below, it requires a number of operation steps, and the slider moving distance is extended, and thereby the cycle time becomes very long.
To shorten this transfer time, the slider may be moved at a high speed. But in such configuration, components of the workpiece conveyer apparatus are worn heavily, and the durability of the apparatus is lowered.
These problems are not limited to the workpiece conveyer apparatus of a surface grinder discussed above, but are commonly observed in other workpiece conveyer apparatuses of machine tools.